The invention relates to a device for sharpening rotary blades, in particular for sharpening blades that turn about a fixed axis of rotation. Rotary blade cutting devices are utilized, more especially, in machines where there is a need for cuts to be effected faultlessly, without tearing the severed material.
Such is the case, for instance, with machines used in the manufacture of cigarettes, where the length of an initially formed cigarette rod constitutes a multiple of the length of the finished cigarette. Accordingly, the blades must be able to cut the multiple lengths into single cigarettes without in any way altering the cylindrical geometry of the product.
As experience has shown, only a slender, accurately sharpened blade is capable of ensuring the perfect cut.
To the end of restoring the cutting edge of rotary blades swiftly and correctly, sharpening devices of current design are envisaged as an integral part of the overall machine, one such device being located beside each rotary blade.
UK Patent 1 173 820 discloses a sharpening device consisting in a pair of grinding wheels disposed with axes parallel and angled in relation to the axis of rotation of the revolving blade. The wheels are convergently conical, and mounted freely to the opposite ends of a rocker pivoted centrally about a fulcrum afforded by one end of an arm, of which the remaining end is pivotably associated in turn with the support structure of the rotary blade assembly. The device comprises a first spring anchored at bottom to the top of the arm and secured uppermost to the support structure of the rotary blade, and a second spring anchored uppermost to the underside of the arm and made secure at bottom to a manual operating lever. The top spring thus functions as a flexible support for the grinding wheels whilst the lower spring cushions the approach of the wheels when offered to the rotary blade. The position of the wheels, angled in relation to the rotary blade, in combination with their conical profile, permits of sharpening the cutting edge to the prescribed bevel from both sides at once.
With this type of device it suffices, whenever the blade requires sharpening, to lower the operating lever by hand to the point where the wheels are brought into contact with the rotating edge, and once it is considered that a sufficient degree of sharpness is achieved, to release the lever.
Clearly enough, a device structured in this manner requires the continual presence of an operator to check on the condition of the rotary blade and to resharpen the edge at suitable intervals.
Where the machine or the equipment is fitted with a plurality of rotary blades, moreover, the operator has to keep a constant check on the sharpness of all the edges.
The task of the operator is complicated yet further where machines are equipped with several rotary blades cutting through different materials, for example filter rod and tobacco rod. In this case, the degree of wear or loss of cutting edge will not be the same for all blades, but variable according to the type of material; for example, the blades which cut through the tobacco rod lose their edge more quickly than those cutting through the filter rod, due to the presence of the tobacco.
In another sharpening device, described and claimed in U.S. Pat. No. 3 010 261, the paired grinding wheels are carried by a sleeve rotatably ensheathing and axially slidable along a mandrel disposed skew in relation to the axis of rotation of the blade. The mandrel is accommodated and restrained internally of the bore of an adjustment sleeve mounted to a supporting bracket, the bracket being embodied in two parts, in such a way as permits of varying the angular position of the adjustment sleeve, hence also the bringing wheels, in relation to the axis of rotation of the blade. The grinding wheels are distanced one from the other in such a way that the rotary blade can be accommodated between them and its cutting edge thus ground from both sides. The wheels are adjusted for position by manipulating the parts of the supporting bracket, rotating the one movable part in relation to the other fixed part, about respective axes.
With this second device, the operator can position the sharpening wheels in relation to the rotating blade and place them in permanent contact with the cutting edge, whereupon the device can be left to operate unminded as the position of the wheels will remain stable. The mandrel is in fact secured by means of clamp bolts, though this tends to lengthen the positioning operation.